Sansui G-8000 (Stereo) Receiver Capacitor replacement.

[RockTheCasbah]

Okay, I have heard quite a bit of many people having upgraded their capacitors on their receivers/amplifiers, and I know that the caps on that G-8000 are probably due for replacement soon, so, what exactly do I want to do here? I have a lot of experience with soldering and such, i just do not know which capacitors to replace, and what are good ones to replace them with...Also, what else should I do in breathing new life into an old receiver?

 

[QuadBob]

Okay, I have heard quite a bit of many people having upgraded their capacitors on their receivers/amplifiers, and I know that the caps on that G-8000 are probably due for replacement soon, so, what exactly do I want to do here? I have a lot of experience with soldering and such, i just do not know which capacitors to replace, and what are good ones to replace them with...Also, what else should I do in breathing new life into an old receiver?

Hi Rock,

Yes you should consider replacing the electrolytic capacitors in your G-8000. There are many different kinds of capacitors.......electrolytic, tantalum, polypropelene, ceramic, etc. etc. But it is only the electrolytics that unfortunately have the shortest "life" of any component used in our cherished equipment. Standard electrolytic caps are rated for 2,000 HOURS of use, or 15 years of "storage life" (ratings courtesy of Nichicon......see www.nichicon.com under technical specifications/application information).

The other components also have a design life expectancy....but they range from hundreds of years to basically infinite DEPENDING on the voltage and current they are subjected to. And, unfortunately.......that goes right back to those electrolytic caps.....as they are most commonly used to establish or regulate DC voltages throughout our equipment. Their second biggest use is as a DC filter........an electrolytic cap will pass an AC (or audio signal) virtually unchanged through itself........but stop any DC imbalance between various circuits. So, you will find them used extensively at the input and output of various circuits for that purpose.

The main problem with them is simply evaporation. As their name implies they contain "electrolyte"......much like the battery in your car. Over the years the electrolyte evaporates and the capacitor dries out. In DC regulation applications this will cause the DC voltage to drop.....so for example a 25vdc power supply will drift ever lower......22vdc, 20vdc, 18vdc etc. over the years. Now, that is bad enough......but the real killer is defined by Ohms Law........as the voltage decreases, Current will increase to compensate (so that the total power remains the same). And, eventually that increased current will blow fuses, burnout transistors, resistors (causing them to overheat and either open or change value), burnout lamps and generally just cause every circuit to self-destruct. And, that is why our now vintage gear in the 20-30 year old range is failing.

In their other application as a DC filter.......the electrolyte evaporation causes the capacitor to change the AC (audio) signal passed through it. Instead of the signal passing through unchanged.......it too is affected by a loss of signal strength, so the output signal is weaker than that input. Additionally, the signal is "squeezed"......it doesn't have the full range anymore. We can hear this audibly as the signal collapes into the midrange.....the highs and lows are lost as the capacitor "filters" more than just DC.....but the actual audio signal also. Even worse.......the capacitor can fail to totally stop DC imbalances.......so you hear "humms" and/or "pops" as the capacitors either "leak" DC, or discharge into the circuit it is supposed to be filtering.

So, should they be replaced? Absolutely...........if you want whatever piece of equipment in question to continue working at all, or more importantly to "sound" like it was originally designed to! Otherwise, throw it away or sell it and buy something "new".......which will give you all new caps at no extra charge!

I'll continue this discussion in the next post to deal with what else needs to be done!! @:

QB

 

[QuadBob]

Also, what else should I do in breathing new life into an old receiver?

Ok......so you've now replaced all approximately 140 electrolytic capacitors in your beautiful G-8000 receiver (I'm guessing.....as I've restored a G-9000, and the G-8000 is basically the same chassis and design).

Replacing the electrolytic capacitors is time-consuming and tedious......but it is actually the easiest part of a true restoration! Once you've got that accomplished.....the real fun begins.

You then need to troubleshoot every circuit that is questionable.....due to the damage already done by those pesky bad caps, you may very well have blown or weak transistors, resistors that are WAY out of spec. (example: I routinely find 180 and 150 ohm resistors in the amplifier stage that read from 250 ohms up 2.2K or even higher!). It is possible that other types of capacitors are either open or shorted also. And the real common pain is "cold solder joints". Again, these can be almost directly blamed on the electrolytic capacitors........as the unit heats and cools from turn-on to shutdown, and as the current flow is increased to compensate for the low voltages.....solder joints will turn dull in color and/or develop hairline cracks. This is the #1 cause for intermittant operation and/or weak signals, or intermittant signal transmission depending on whether the unit is "hot" or "cold".

So, get out your trusty soldering iron......and replace every other bad or questionable component as necessary. Clean and resolder every cold solder joint, and you'll be ready for the final step!

Ok.....everything that needs to be replaced is replaced, all the solder joints and wiring connections have been resoldered as necessary. Now you just need to do a complete calibration and alignment! You can start with the Power supplies, then do the amplifier section (DC offset and bias), the Tuner section.....and if its a quad piece, then any onboard decoder or demodulator!

After accomplishing all the above.......you'll find that cleaning off 20 plus years of dust, grime, and dirt......is really a piece of cake!!! Of course that includes either cleaning, replacement or repair of all switches, pots and other controls as necessary.

Now you've got yourself a "classic" piece of vintage gear that should pretty much look and more importantly sound.......like it was built yesterday instead of 20 or 30 years ago!

QB

 

[QuadBob]

And a couple of things I pretty much skipped over:

1) You'll need a copy of the factory service manual and schematic. Without it.....your dead.

2) If you can't read or understand the service manual and schematic.......you're dead.

3) You'll need to completely (or almost completely) disassemble the unit under examination.....at least to the point where you can access BOTH sides of EVERY circuit board.....as you'll need to solder on one side of the board, and remove/install the components on the other side.

4) You'll need to develop what I call a "cap list" to order the new caps required...noting their voltage and capacitance rating. The service manuals don't have this information (or at least they're never complete and accurate!). So, you need to examine every board and every nook and cranny and develop the list yourself. Depending on your visual accuity...be ready with a magnifying glass! Also, you have to be ready to make "allowable" substitutions.....as quite often the exact rating you need is no longer available. Higher voltage ratings are OK........lower is a NO NO!! Capacitance ratings should stay the same.....EXCEPT where the cap is being used as a DC voltage stabilizer......in which case higher ratings are OK (the circuit will only charge the cap up to its design rating.....regardless of the caps value)

5) Get ready for a scavenger hunt for any other bad components.....they are getting harder and harder to find. Many of the transistors are now obsolete, Sansui liked to use 7 and 8 volt lamps.......which are becoming near impossible to find (today everything is 6 volts or 12 volts). Of course switches and controls can either be easy.....or impossible, just depends on what it is and whether it is still in common use.

6) You'll need any and all required test equipment as noted in the service manual.....digital volt meter, oscilloscope, signal generator, and for the quad units and decoders......sources for test signals, etc.

7) An ever expanding music library to enjoy while you spend hours and hours either soldering or studying cross-reference and source books to find that last damn transistor you need!

QB

 

[RockTheCasbah]

Whoa...okay, The capacitors I understand..Soldering is a breeze, I can read and understand service manuals and schematics just fine. And of course any monkey can clean up 20-year old yuck. But the last post and a half just scared me..and I do not have an oscilloscope.. I understand you have a good reputation for doing this kind of work, bob. How much would you charge for this? I'm used to repairing all kinds of things, but this is a bit too complex..

 

[RockTheCasbah]

Oh yeah, I understand that polypropolene caps are of better quality than the electrolytic caps. I'd like this thing to have a little upgradedness to it if that's possible.

 

[timw]

QB, Very interesting posts. Great explanation of all that's involved in this kind of restoration. I have a quick question for you(speaking of capacitors...). I need to replace the (2) large 'can' type caps in one of my Adcom Monoblock amps. Unfortunately, Adcom parts dept doesn't stock them anymore. Do you know of a good place to look for these online??? They are labeled 35000uf / 125v surge and are just a little smaller than a soda can.
I appreciate any help you can provide!
Thanks, Tim

 

[john e. bogus]

"But the last post and a half just scared me..and I do not have an oscilloscope.."

If you're able to read a schematic and understand the service manual, then you should NOT be getting scared at this point! If so, you have several options: 1) You can still replace the caps and clean everything up as a minimal restoration....as you said, any monkey can do it....then take it to an experienced tech for alignment / repair.....replacing caps and cleaning is where all of your time goes on this project, so you can cut the cost quite a bit if you do at least these things yourself. 2) You don't absolutely NEED a 'scope, but it sure makes life easier if you have one and know how to use it! (you can get an older used one suitable for audio work quite cheaply....I paid $5 for mine) The caps, resistors, transistors, and diodes can all be checked using nothing more than a VOM....you can buy one that is more than adequate for the job in the $25-50 price range. A 'scope is only used for working on "live" circuits, it allows you to view an AC waveform and is not used in most regular alignment proceedures, but will make some repairs MUCH easier if you know how to use it. In other words, you really shouldn't need a 'scope, especially if you have a receiver that is already working properly and is not in need of repair. 3) You can always wade right in and learn whatever you don't know as you go! (especially if you have other good working gear to use in the meantime) Don't be afraid to make mistakes, although as Bob notes, some of them might prove rather difficult to correct....whatever you learn will make your next project that much easier....

"I understand that polypropolene caps are of better quality than the electrolytic caps"

Not necessarily better....they both do a different job. Non-electrolytic caps are usually used to pass a signal rather than filter DC. They also degrade over time, all non-electrolytic caps do, but the problem is not nearly as bad as with electrolytic and paper / oil type caps. Electrolytic caps should be replaced only with electrolytic caps. Polypropolene caps can replace everything else. Low pf values beyond the range of most poly caps can be replaced with silver mica NP0 types.

"I'd like this thing to have a little upgradedness to it if that's possible."

Just use good quality new parts from a reputable manufacturer and upgrade the tolerances and ratings of the components by as much as you can afford or are willing to pay.....

"parts dept doesn't stock them anymore. Do you know of a good place to look for these online???"

I use Digikey, Antique Electronic Sales, and Surplus Sales Of Nebraska....all are reputable outfits who have been in business for 20 years or more, and there's plenty of other good suppliers out there.....if a parts house dosen't have what you want listed in their catalog, but is a distributor for the manufacturer of a part you need, try the manufacturer's website, you may be able to order a manufacturer's part number not shown in the distributer's catalog. Get used to having to make parts substitutions, and lots of searching around to find parts (caps especially) of the correct values that will fit in the gear without physical modification.....

One small comment is that I would NOT recommend replacing caps in the frequency-determining circuits in the RF portion of the tuner section! This will make the difference as to whether you only have to do a quick touchup or a total overhaul of the RF alignment and tracking of the tuner....

Yours Truly,
john e. bogus

 

[QuadBob]

Whoa...okay, The capacitors I understand..Soldering is a breeze, I can read and understand service manuals and schematics just fine. And of course any monkey can clean up 20-year old yuck. But the last post and a half just scared me..and I do not have an oscilloscope.. I understand you have a good reputation for doing this kind of work, bob. How much would you charge for this? I'm used to repairing all kinds of things, but this is a bit too complex..

Hey Rock,

Thanks for the comments. And, you're correct......it isn't rocket science (or even an Xray System! ) so they sometimes go fairly straight-forward through the process......other times they become bottomless pits of hours and hours of time, searching and parts. The problem is that you won't know that until you get into the middle of it!

When I restored the Sansui G-9000......I assumed it would be a MUCH simpler restoration than the QRX-9001.......after all it was ONLY a stereo receiver! Well, this particular unit was obtained off of EBay, had been physically damaged in shipment.....and even worse, at least two other "audio repair" guys had attempted to fix it. It came to me with the physical damage and a blown left channel (including a burned driver pcb and all the output transistors shorted or open). Well, let me tell you...each channel used 4 output transistors that ran $15.00 each......so $60 per set, I went through over $300 worth of them troubleshooting the driver circuit. It got to the point where I had EVERYTHING checked and verified......then was afraid to turn it on, as usually within 5 minutes of operation I'd see the smoke starting! @: As it turned out......during one of the previous repairs, one of the pairs of output transistors was substituted for what "should" have been an acceptable replacement........except that it WASN'T! The current draw and gain were too different from the original design.......and thus it would simply self-destruct when placed under a load! Of course I didn't realize this until AFTER going through numerous sets of output transistors, rebuilding the driver circuit repeatedly, then spending hours studying the cross-reference manuals and original schematic.......it wasn't until I reviewed the actual specifications for each of the transistors that I realized what was happening. Finally, it did come out great......no more problems and a happy owner, but it sure wasn't easy getting there!

Currently I'm swamped with restorations, so I really don't want to take anything else in until I get caught up to date. I'll be happy to let you know once I've cleaned out my "in" shelf!!

QB

 

[RockTheCasbah]

Hmm, well the receiver itself in it's current condition works okay except the pots are scratchy. I'll either clean or replace those within a week after I get it. (I pick it up on the 21st, when i get back home from florida), so I'm guessing all i'll wanna do is change out the caps, and pull out my VOM and test everything i can. I'm going to pick up a service manual immediatly too. Hmm..then I guess it should be okay if i'm not recalibrating anything. But how much do caps usually cost?, Oh yeah, and thanks for all the advice guys. You guys rule!

 

[proufo]

Hello RTC.

Check this thread:

https://www.quadraphonicquad.com/forums/showthread.php?t=2616

Best regards.

 

[RockTheCasbah]

Hmm..I'm still a little lost in terms of what exact ones I'll need..or where to get them, and what type? KG, NX, ?